If the first non-blank character of a line starts with #,
the command is ignored.

Commands are split at whereever ;; appears.
This process disregards any quotes or other symbols that have meaning in Perl.
The strings after the leading command string are put back on a command queue.

When reading a command if the string ends in \ (backslash),
another line is read and this is concatenated to the previous result with a newline inserted between the prior string and the continuation string.

Within a single command,
tokens are then white-space split.
Again,
this process disregards quotes or symbols that have meaning in Perl.
Some commands like eval,
macro,
and break have access to the untokenized string entered and make use of that rather than the tokenized list.

Resolving a command name involves possibly 4 steps.
Some steps may be omitted depending on early success or some debugger settings:

The leading token is first looked up in the macro table.
If it is in the table,
the expansion is replaces the current command and possibly other commands pushed onto a command queue.
See the "help macros" for help on how to define macros,
and "info macro" for current macro definitions.

The leading token is next looked up in the debugger alias table and the name may be substituted there.
See "help alias" for how to define aliases,
and "show alias" for the current list of aliases.

After the above,
The leading token is looked up a table of debugger commands.
If an exact match is found,
the command name and arguments are dispatched to that command.
Otherwise,
we may check to see the the token is a unique prefix of a valid command.
For example,
"dis" is not a unique prefix because there are both "display" and "disable" commands,
but "disp" is a unique prefix.
You can allow or disallow abbreviations for commands using "set abbrev".
The default is abbreviations are on.

If after all of the above,
we still don't find a command,
the line may be evaluated as a Perl statement in the current context of the program at the point it is stoppped.
However this is done only if "autoeval" is on.
(It is on by default.)

If auto eval is not set on,
or if running the Perl statement produces an error,
we display an error message that the entered string is "undefined".